1. Field of the Invention
The present invention relates to image processing apparatuses and image processing methods, and more particularly relates to an image processing apparatus and an image processing method suitable for a facsimile apparatus or the like including a recording unit using an ink-jet recording system.
2. Description of the Related Art
Recently, color facsimile communication has been standardized by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), and facsimile apparatuses for compressing and communicating a color image in a Joint Photographic Experts Group (JPEG) compression system are well known. A recording unit in this type of facsimile apparatus is provided with a recorder using a laser beam system or using an ink jet system. In particular, facsimile apparatuses with a recording unit using the ink jet system capable of recording color images at low cost are widely disseminated.
Image recording apparatuses using laser systems, and particularly those using ink jet systems, have ink droplets of uniform size for recording a solid black portion when recording a thin line. The conventional image recording apparatuses are disadvantageous in that ink droplets of a size adequate for clearly recording the thin line are excessive for recording the solid black portion. Although it may depend on the quality of the paper or on the recording environment, an ink droplet for one dot tends to bleed in the paper, thus printing on an area larger than the target resolution of one dot. This problem is caused by characteristics of ink-jet recording, and the excessive ink noticeably accumulates in the black solid portion.
Due to the excessive amount of ink, an image, immediately after being printed, is output which is black and wet due to the ink. This may cause smearing which may spoil a next page, and the ink may soil a user. The excessive ink may also cause the paper to kink and crinkle. This causes waste not only of ink for recording but also of power consumption for recording.
Accordingly, there has been proposed an apparatus for decimating recording dots so as to conserve ink to be used and to reduce power consumption during recording, and to provide countermeasures against black-wetting and smearing. The user can set the apparatus to perform decimation, thus reducing ink consumption and the operating cost.
Decimation includes two types of processing. One is unconditional decimation for unconditionally zigzag-converting black pixels into white pixels. The other is reference-conditional decimation, as disclosed in Japanese Laid-Open Patent No. 8-130637, for referring to states of pixels adjacent to a pixel to be decimated and for determining whether to decimate the pixel.
Hitherto, once the user has set the apparatus in a decimation recording mode, the apparatus always performs decimation regardless of the type of image to be recorded, whether it is a monochrome character image, a monochrome halftone image, or a color image.
The monochrome halftone image and the color image are images obtained by printing beautifully pictures and photographs. When a subject-copy image is read and converted into recording data, that is, binary data, halftoning, such as error diffusion processing, is performed.
For example, when multi-valued color image data obtained by reading a color subject copy is converted into a binary color image, color-difference data generated by peripheral conversion is added to the multi-valued color data. Subsequently, the added data is converted into a predetermined single color by comparison.
When the recording unit decimates and records the processed recording data, gray scaling and overall color balance are lost, thus providing the user with an undesirable output image.
Since the monochrome halftone image is binarized by error diffusion processing, the image will lose gray scaling when decimated and the image quality becomes substantially degraded.